54 PLANT LIFE ON THE FARM. 



in wide cttrves till they come in contact with a support 

 round which to twine,* and thus remove their leaves 

 from the surface, where they would be overshadowed, to 

 a point of vantage where they would be exposed to light, 

 and this with the least expenditure of material. Very 

 similar are the movements executed by stolons and run- 

 ners, as of the strawberry, and probably, though the 

 cases have not been studied, of the trailing rhizomes of 

 the twitch (Triticum repens), the scions of the meadow 

 poa (Poa pratensis), of the clovers, of the milfoil, etc. 

 Such a movement would facilitate the introduction of 

 these runners between other plants, and thus secure the 

 extension of their area of growth. The movements in 

 the stem are more especially connected with growth ; 

 they cease, or become much enfeebled after growth is com- 

 pleted or arrested. Under certain circumstances, however, 

 the faculty of growth is retained in certain spots after it 

 has ceased elsewhere, or if actual growth do not take 

 place, yet some of the phenomena connected with it may 

 occur. Thus the stems of grasses, such as of wheat, are 

 provided with thick "nodes" or joints at the places 

 whence the leaves spring from the stem. When the 

 wheat gets beaten down or laid by a storm of rain and 

 wind, the resumption of the erect position is effected by 

 the medium of the nodes, which grow, or at least become 

 turgescent, especially on the under surface, which thus 

 becomes convex, while the upper surface, which does not 

 grow, or at least not to the same extent, becomes con- 

 cave ; the consequence is that the upper end of the stem 

 becomes raised as may be illustrated thus : Let- 

 represent the joint of the laid stem ; then, by the agencies 

 just mentioned, the straight horizontal position is replaced 



by the ascending one , and ultimately by the vertical one 



*See Darwin, The Movements and Habits of Climbing Plants, 



